A plurality of unit pixels (unit cells) are arranged in rows and columns in an imaging area of a CMOS image sensor. For example, Jpn. Pat. Appln. KOKAI Pub. Nos. 2000-125209 and 2005-286565 disclose a CMOS image sensor, in which each unit pixel is provided with a high-sensitivity photodiode and a low-sensitivity photodiode and thereby a signal electric charge dealing quantity (dynamic range) of pixels is enlarged.
The dynamic range of pixels is determined by a saturation level of photodiodes of pixels of a specific color, and pixels of colors other than the specific color cannot be used to the saturation level. For example, in RGB sensors provided with color filters of an RGB Bayer arrangement which is generally used, sensitivity of G (green) pixels is the highest, and the G pixels reach the saturation level first when light is made incident. At this point in time, B (blue) and R (red) pixels other than G have not reached the saturation level. In this case, the dynamic range of the whole pixels is restricted by the dynamic range of the G pixels.
As described above, also in conventional sensors aimed at expansion of the dynamic range of the pixels by providing each unit pixel with a high-sensitivity photodiode and a low-sensitivity photodiode, the dynamic range cannot be further expanded, since it is not considered that the sensitivity of pixels varies according to colors.